The original version had a very sharp gain control which seemed to go from off to wide open by turning up the gain just slightly. High plate voltage, nice power amp compression.
Rev2 had a smoother gain structure. High plate voltage, nice power amp compression.
Blue Revision is a brighter and tighter sounding amp. Lower plate voltage.
I have a Rev2 and love it. It is my "go to" amp without a doubt. Can't see me wanting any other version of it, except maybe the new version with the power amp tuning and KT88's, but that is a big maybe.
Both the original and rev2 have some nice power amp compression/sag which I like a lot.
Hope that helps.